This design allows attaching a 2-liter bottle to a resin bottle. The 2-liter bottle can be cut and used as a funnel to drain the SLA printer resin vat back into the resin bottle. The 2-liter bottle makes a great funnel and is large enough to have a filter placed inside. The adapter is threaded for both the 2-liter bottle as well as the resin bottle.

I had seen funnels that were made from 2-liter bottles, but I found them to be prone to falling over since it would just sit on the bottle. I decided to make and adapter that would thread onto the resin bottle as well as the 2-liter bottle. This way the funnel could not fall off.

I designed this with a little extra clearance so that it threads onto both bottles easily. It does not need to seal, just mount on the bottles and not fall off.

I have printed this with both FDM and SLA printers. 

• For the FDM print, I printed it upside down (tapered section at the bottom) and use an outer brim. No supports were needed.
• For the SLA print, I also printed it upside down and tilted at a 45-degree angle.

Danger, technical details for makers!  Who knew bottle thread forms were so involved! 

Since it took a lot of research and experimentation to get the thread forms correct, I thought I would share my findings. The 2-liter bottle uses a PCO1881 thread. The following links are for the details of the thread spec. After a lot of analysis, I determined that the resin bottle uses the PCF-38P-4 thread form (or a variation of it).

Soft drink bottle top thread sizes (imajeenyus.com)

ISBT - ISBT Threadspecs Downloads

3784253-21.pdf (isbt.com)  ← PCO1881

pcf38p4.pdf (isbt.com)   ← PCF-38P-4